Glass-lined steel equipment is manufactured by repeating the steps of applying glass material on a steel substrate of the equipment, heating the entire equipment at a high temperature in a furnace so that a continuous glass layer having a thickness of about 1 to about 2 mm is fused onto the steel substrate.
Glass-lined steel equipment exhibits the mechanical strength of the steel substrate as well as the resistance to corrosion and smoothness of the glass layer, so that glass-lined equipment such as vessels, reactors, and their accessories are widely used in the chemical, pharmaceutical and food industries. However, during service, the glass layer may be damaged locally by an inadvertent operational error that causes the formation of a crack or exfoliation in a portion of the glass layer.
If such damaged portion of the glass layer remains unrepaired for a further period of operation of the equipment, the corrosion of the steel substrate underlying the damage area will be accelerated and the materials contacted by the corroded metals can be contaminated causing a serious problem. It is thus desired to repair, at its place of installation, any local or partial damage to the glass layer as soon as possible.
Typical methods of local repairing of glass-lined equipment include:
(a) a method of using caps or bolts of anticorrosive tantalum material, in which TEFLON.RTM. packings are employed for sealing between a glass layer and the tantalum caps or bolts (See U.S. Pat. No. 2,631,360); and
(b) a method of applying an anti-corrosive adhesive of an organic resin, such as an epoxy resin or the like;
However, their respective disadvantages are:
(a) for the tantalum repair method, there is
difficulty in providing caps or bolts that
correspond in configuration to an extended damage area, and the TEFLON.RTM. packings may be degraded causing penetration of impurities; and
(b) for the epoxy resin repair method, the resistance of epoxy resins to heat and solvents are low and inferior so that the further use of the repaired equipment is very limited.
A sol-gel process is known in which an alcohol and water solution of an organo metallic compound, such as a metal alkoxide which serves as a starting material, is heated at a relatively low temperature for solidification (via a dehydrolysis reaction and a condensation reaction to form a glass); thus, glass can be obtained at a much lower temperature than conventional melting process. However, a repair method using the known sol-gel process to repair a damaged glass layer requires a considerable length of time for heating for the required hydrolysis and condensation, and the generation of glass. Further, the known sol-gel process produces considerable shrinkage during solidification that often causes a crack or exfoliation in the formed glass layer. In order to produce a glass layer in accordance with the known solgel process without cracking, the formed glass layer should have a thickness of at least about 1 um and solidification requires a period of time of about one month. The cracking during solidification should be eliminated for satisfactory repair.
It is also understood that in the known sol-gel process, the higher the temperature for heating, the more the hydrolysis and condensation reactions of the repair agent are accelerated, to cause a resulting solid to be more closely bonded.
The heating of the repair agent should be effected at a temperature of less than but approximate to 350.degree. C., which is about an upper limit, allowing a stress on the glass layer to remain without shifting from compression to tension due to the difference in thermal expansion coefficients between the steel substrate and the glass layer.
It is also known that for the purpose of heating a resin repair agent within a small space in glass-lined steel equipment, such as a reaction vessel, a hot-air heater or infrared heating lamp is commonly used. However, in practice, the heat is dissipated beyond the area to be repaired and thus, the thermal efficiency is low. Accordingly, the heat at the resin may not reach approximately 350.degree. C. and the working conditions in the equipment will be degraded due to heat dissipation.
Accordingly, to successfully repair a damaged portion of the glass layer of the equipment, without damage to the glass layer at areas adjacent to the damage or repair point, the following factors are important:
(1) to readily increase the temperature at the area to be repaired, up to about 350.degree. C., and maintain the temperature for a period of time sufficient for solidification of a repair agent;
(2) to keep the thermal dissipation at the repair area to a minimum for repair operations within glass lined equipment; and
(3) to provide a repairing apparatus and method which ensures flexibility so that the repair agent or material can be provided to correspond intimately in configuration to intricate surface configurations of the repair area of the glass layer.
The present invention is thus directed to solving the foregoing problems in providing a method and an apparatus for repairing a damaged portion of glass-lined equipment.
More particularly, some aspects of the present invention include:
(1) avoiding cracking or exfoliation caused by heat shrinkage during solidification of a repair agent by using a repair agent mixed with an inorganic filler material;
(2) developing a glass layer repair material having less voids by means of a void filling process including impregnating a liquid agent into the voids generated in the outer-most surface of the glass layer, so that the voids are filled with the impregnating liquid which is then heated to form a glass;
(3) developing a phosphate glass layer at the bottom or steel-contacting surface of the repair layer, which has a high adhesive strength for the steel substrate;
(4) developing a repairing layer of glass by adhering a sheet of inorganic filler material to the damaged area of a glass layer; and applying a repair agent onto the inorganic filler sheet which is solidified into a glass by a sol-gel process, for the purpose of reducing the number of repeated cycles necessary to form a glass layer of a desired thickness;
(5) developing a smooth surface on an upper surface or top layer of the repair layer, by applying onto the repair layer a repair agent which contains a filler of a fine powder, having a particle size less than about 1 um in diameter, and heating the same; and
(6) maintaining the temperature for heating a repair agent within a given range (from about 300.degree. C. to about 350.degree. C.) which causes essentially no tension in the existing glass layer which is thus protected from cracking or falling off in an area adjacent to the damaged area.